1. Field of the Invention
This invention relates generally to hydrodynamic seals, and more particularly toward the formation of a sealing element having improved flexibility.
2. Related Art
Hydrodynamic seals are used frequently as an interface between a housing and a rotating shaft where it extends through the housing to contain oil, water or other fluids against leakage. These types of seals are sometimes referred to as radial shaft seals. Common applications for hydrodynamic seals include engine crankshafts, transmission shafts, as well as a variety of industrial applications.
Hydrodynamic seals typically include an elastomeric member in direct contact with the rotating shaft. In some varieties of radial shaft seal, this elastomeric member is made from polytetrafluoroethylene (PTFE) type material. Of course, other suitable alternative materials may exist. The PTFE elastomeric sealing member is designed to deform in use so as to enhance the likelihood that the seal will stay in continuous, intimate contact with the rotating shaft despite any lack of concentricity between the rotating shaft and the seal's carrier structure.
Many examples of hydrodynamic seals with PTFE sealing members are shown in the art. For example, U.S. Pat. No. 6,168,164 to Toth et al., issued Jan. 2, 2001 describes a hydrodynamic seal with a PTFE element that includes specially formed hydrodynamic grooves. The entire disclosure of U.S. Pat. No. 6,168,164 is hereby incorporated by reference and relied upon. Another example of a prior art hydrodynamic seal may be found in U.S. Pat. No. 7,100,924 to Toth et al., issued Sep. 5, 2006. The entire disclosure of U.S. Pat. No. 7,100,924 is hereby incorporated by reference and relied upon. The '924 patent describes a PTFE hydrodynamic sealing element which, in one embodiment, includes an integrally formed living hinge portion for enhanced sealing element flexibility. This reference describes the long felt need for seal flexibility in these applications. A further example is shown in U.S. Pat. No. 6,336,638 in which a continuous open groove spiral is coined into both a common thickness mid-portion and inner region seal element.
While the hydrodynamic seal constructions shown in at least some of the above noted patents have been commercially successful, there remains a continuous desire to improve the seal construction so that it functions even more efficiently. Three areas of particular concern for improvement relate to the flexibility of the sealing element, dirt exclusion, and air leak testing. In some applications of hydrodynamic seals, for example in engine crankshaft applications, a newly assembled engine is leak-checked using air pressure as a quality control measure. While hydrodynamic seals according to the prior art designs like those described above function well in service, they are not always well-suited to these newer leak-checking methods in which an engine block is pressurized with air. The large open groove of some prior art hydrodynamic seals are not well suited to these newer leak checking methods. The large open groove of the seal element has been identified as contributing to the cause for leak-check failure. Accordingly, there is a need to provide an improved hydrodynamic seal which functions well in normal operations and is also suitable to holding pressurized air in an engine block, for example, during leak-checking procedures. Also, seal elements with continuous large open groove spirals like that shown in U.S. Pat. No. 6,336,638 have a problem with the suction of external dirt and dust being pulled under the sealing lip interface at the shaft, allowing dirt to pass into the oil chamber and wear the shaft.